pic: Plywood 8WD Concept

[z_beeblebrox]

Some more specs not in the original post:

-Estimated weight of 34.8lbs (Wood frame weighs 8.8lbs)
-Geared 5.82:1 for an adjusted top speed of 12.9 ft/s
-Wheels, belts and pulleys accessible from bottom of robot
-Includes mounts for encoders, battery and main breaker

Here's another view with the top plate removed so it's easier to see the structure and power transmission components:

Originally Posted by Kevin Leonard

Can I ask why this is specifically a plywood drivetrain? It looks to me like a sheet metal drivetrain. What makes it plywood?

And what design decisions were made knowing it would be made of plywood instead of some metal?

Our team has a sheet metal sponsor, but they have about a week turnaround time. We also have a laser cutter in-house which cuts plywood so if we use wood, we can get our parts much more quickly.

IMHO, the main design differences between plywood and sheet metal are the material thickness, the method of attachment and the lack of bends in wood.
-The drivetrain is made out of .25" plywood; if it were aluminum, I'd use .060-.090".
-Instead of being riveted like sheet metal, the drivetrain will be assembled with finger joints (http://www.instructables.com/id/How-...at-Right-Angl/) and glued.
-You can't bend wood like sheet metal so every section at a different angle is a separate piece. The wood frame has 28 parts; with bent sheet metal, far fewer would be needed.

Otherwise, I think designing for plywood and sheet metal is quite similar, since both are very strong in the plane of the material but vulnerable to cracking or bending if force is applied from other angles.

Originally Posted by Woolly

It looks like for each corner wheel there's a vexpro pulley towards the frame perimeter on the shafts for the wheels set further inside the frame, and a pully towards the center of the frame on the shafts for the wheels further towards the edge of the frame perimeter. It also seems like there is a gap in the plywood for the belts to run through that is hard to see in this rendering due to perspective.


Though that does bring up another thought. Is there any quick and easy way of adjusting the tension of the belts, such as a vexpro versablock and cam setup?

Also, another thing I noticed, was that the lightening hole behind the inset wheels happens to line up just right so that debris could be thrown by the wheels right up into your drive-train gearboxes and potentially your electronics.

Wooly is correct in his description of the powertrain components.

There is not a tensioner for the belts; we had good experiences with center-center distance belts on the AM14U last year and would be happy to use them again.

Good catch about the lightening hole; I'll remove that in the next iteration.

Originally Posted by Rauhul Varma

You have the perfect place to mount fans above the cims, while I do not think they are very useful during competition, if you were to make a practice bot that would be running for extended periods they could be very valuable. Just my 2 cents.

Good idea. I don't have CAD of a fan to add now, but if we built something like this, I would figure out mounting for a fan.

The next thing I'd like to look into is repackaging a ball shifter into a lower and thinner enclosure to add a lower gear to this drivetrain. I'm also worried about the loads on the CIM pinions in the current gearbox.